1. Field of the Invention
The present invention relates to a machining method of a part with a laser-clad metal to be formed with a valve seat portion in a cylinder head of an engine.
2. Description of the Related Art
Aluminum-based alloys which allow lighter weight as compared with steel are used as material for a part for an automobile such as a cylinder head of an engine. However, it is difficult to secure strength in high temperature or abrasion resistance for the aluminum-based alloys. For example, there occurs a problem that an aluminum-based alloy is applied to a portion which is exposed to combustion gas with a high temperature, such as a valve seat portion. As a technique for improving heat resistance or abrasion resistance of a specific portion of an aluminum-based alloy part, there has been known a technique for irradiating laser beam on alloy powder with such an excellent property as excellent heat resistance or excellent abrasion resistance to clad the specific portion with the alloy.
An inspection is made by an eddy current examination apparatus about whether or not there is any internal defect such as a crack or a pore in the laser clad portion. Since a control surface which has been machined is required for making an exact examination, the eddy current examination is usually performed after a final product shape has been obtained.
When any defect has been detected, it is required to remove a surface layer having the defect in a grinding manner and to clad the portion with another metal. However, after a final product shape has been achieved, an extra metal positioned on a inner peripheral side has been removed, so that an amount of clad metal required can not be secured. That is, even though a defect has been found after the final product shape has been achieved, it is impossible to readjust the final product shape.
A cylinder head of an engine in an automobile generally comprises a plurality of valve seats. In a case that a defect has been detected in only one of these valve seats, even when there is not any defect in the remaining valve seats, the cylinder head must be scrapped as a defective article or product. This is a significant obstruction factor against improvement in production efficiency of a cylinder head.
The present invention has been attained in order to solve the above problems, and an object thereof is to provide a forming method of a part with a laser-clad metal for improving a production efficiency of a valve seat portion in a cylinder head for an automobile.
According to the present invention, immediately after a laser cladding is achieved, the portion is machined to form a control surface while an extra metal remains on an inner peripheral side of a base metal constituting a joint portion between a valve seat portion and a port. An intermediate inspection is made using the control surface about whether or not there is any defect in the clad metal. When a defect is detected, the deposited metal is removed and another laser cladding is achieved. Since there is the extra metal capable of securing an amount of clad metal required, even when a defect has been detected in the intermediate inspection, a readjustment can be made. Therefore, the production efficiency of a valve seat portion in a cylinder head for an automobile can be improved.